658 R. PUMPELLY EVOLUTION OF OASES AND CIVILIZATIONS 



During a dry period preceding the founding of the north kurgan, a 

 valley had been cut in the delta-plain, the surface of which dated from 



Grovelwilho miiliw loess-forming time. 



£rl°:;,lV Then came a period of increased precipitation, 

 during which the valley was refilling during the life 



b— ,oo~ i? of the oldest culture and into that of the second. 



| During part of the second culture — the latter part 



S*»- 2 of the life of the north kurgan — there recurred a dry 



bTI,^ I period during which the valley was reexcavated. 



B 11,o«-. ^ When, under renewed precipitation, it began to refill 



SKa.-^"*-" .§ again, the south kurgan was started on the west side 



L„.„„ iH .c.b W „ | of the valley, on the orignal loess-plain. This 



jgSrSsr ? growth of sediments continued till it rose higher than 



IIX"!.. * the previous aggrading, overflowing not only the ter- 



«..« .«.'.«« x ra ce of this and the general plain, but also a part of 



sassiss, $ ^ ne eai> li er culture of the growing south kurgan; and 



^ it continued to grow until the flourishing period of 



a the life of this kurgan was drawing to a close, at a 



Bos-*— £ height of 52 feet above its base. 



B,o„„,oo m § Then followed again a change to dryness, causing 



Z the reexcavation of the valley and lasting through the 



£ life of the supposed barbarian occupation. 



cobbies | Again a reverse change caused the refilling (shaft 



e^ ...a,- £ g\ ^ a ^ followed, which lasted till the introduction 



L a r,„.«,.oa m g °f irrigation, and this period of refilling coincided 



| with the life of the Iron culture. 



Br0 ~ ,,,o "~ . The coincidence is thus very marked between the 



| founding and growth of cultures and the conditions 



Cobb '" 45 of precipitation that permitted the aggrading of this 



J part of the delta; and equally well marked is the 



S™* £ relation between the dry periods and the disappear- 



1 ance of cultures. 



CO 



f In the accompanying table, figure 6, R. W. Pum- 



I. pelly has attempted to correlate the march of human 

 g and physical events during Quarternary and recent 



2 time. 

 The record in the Askabad well (figure 7) is very 



interesting, for it gives a section extending 2,300 feet 

 down in the zone of deposition and depression. 

 Below the upper 60 feet, with the exception of layers of coarse material 

 aggregating less than one-tenth of the volume, it consists uniformly of a 



